SDAG TailCall Debug

llc < reproducer.ll -debug-only=isel -mtriple=x86_64
=== caller
Initial selection DAG: %bb.0 'caller:entry'
SelectionDAG has 12 nodes:
  t0: ch = EntryToken
  t2: i64,ch = CopyFromReg t0, Register:i64 %0
  t5: i64 = GlobalAddress<double (double)* @callee> 0
    t4: f64,ch = CopyFromReg t0, Register:f64 %1
  t7: ch,glue = CopyToReg t0, Register:f64 $xmm0, t4
  t11: ch,glue = X86ISD::TC_RETURN t7, TargetGlobalAddress:i64<double (double)* @callee> 0, Constant:i32<0>, Register:f64 $xmm0, RegisterMask:Untyped, t7:1